2-octyl (meth)acrylate adhesive composition

ABSTRACT

A pressure sensitive adhesive composition comprising a 2-octyl (meth)acrylate/(meth)acrylic acid copolymer is described. The adhesive composition may be derived from renewable resources and provides good peel, shear and high temperature stability.

CROSS-REFERENCE TO RELATED CASES

This application is a continuation of U.S. patent application Ser. No.11/549,162, filed Oct. 13, 2006, the disclosure of which is hereinincorporated by reference.

BACKGROUND

Pressure sensitive adhesives (PSAs) are known to possess propertiesincluding the following: (1) aggressive and permanent tack, (2)adherence with no more than finger pressure, (3) sufficient ability tohold onto an adherend or substrate, and (4) sufficient cohesive strengthto be removed cleanly from the adherend. Materials that have been foundto function well as PSAs include polymers designed and formulated toexhibit the requisite viscoelastic properties resulting in a desiredbalance of tack, peel adhesion, and shear holding power. PSAs arecharacterized by being normally tacky at room temperature (e.g., 20°C.). PSAs do not embrace compositions merely because they are sticky oradhere to a surface.

Only a limited number of classes of polymers have been found to functionas PSAs. Among these polymer classes are natural and synthetic rubbers,(meth)acrylic polymers, silicones, block copolymers and olefins. Acrylicpolymers have proven especially useful. Acrylic based PSAs arefrequently prepared from isooctyl acrylate or 2-ethylhexyl acrylate.These adhesives have many desirable attributes such as high peeladhesion when applied to a wide variety of surfaces. Acrylic PSAs,however, do not typically provide high thermal stability and will slowlydegrade upon exposure to higher temperature (e.g., above 125° C.).Thermal degradation of these known acrylic adhesives at highertemperatures reduces the cohesive strength of the adhesive and maygenerate bubble formation from high levels of outgassing, resulting in aloss of adhesion. It is desirable to provide silicone-free PSAs thatwill strongly adhere to surfaces at temperatures up to at least about175° C. or even higher temperatures.

Further, acryclic PSAs are generally derived from petroleum feedstocks.The increase in the price of oil, and concomitant petroleum-derivedproducts, has led to volatile prices and supply for many adhesiveproducts. It is desirable to replace all or part of the petroleum-basedfeedstocks with those derived from renewable sources, such as plants, assuch materials become relatively cheaper, and are therefore botheconomically and socially beneficial. Therefore, the need for suchplant-derived materials has become increasingly significant.

SUMMARY

The present invention provides an adhesive composition derived fromrenewable resources. In particular, the present invention provides anadhesive composition derived, in part, from plant materials. In someembodiments, the present invention further provides an adhesive article,wherein the substrate or backing is also derived from renewableresources. The pressure sensitive adhesive composition comprises a2-octyl (meth)acrylate/(meth)acrylic acid copolymer and a crosslinkingagent. The pressure sensitive adhesive of the invention comprises thereaction product of the same. As used herein (meth)acrylate or(meth)acrylic is inclusive of methacrylate and acrylate.

The present invention provides a pressure sensitive (meth)acrylicadhesive that may be useful for adhering substrates that are exposed tohigh temperatures. The adhesive exhibits low outgassing or weight lossat elevated temperatures. Surprisingly, the adhesive of the inventiontypically exhibits a total weight loss of no greater than about 5 wt. %after 3.5 hours at 175° C. as determined by the test method described inthe Examples. The adhesive composition may be extruded, coated, orsprayed directly onto a substrate or surface that is to be bonded toanother substrate or surface.

The invention also provides adhesive articles such as tapes and the likecomprising a layer of the foregoing pressure sensitive (meth)acrylicadhesive disposed on a support or backing. The support may be a releasesubstrate or liner to provide a so-called transfer tape wherein theexposed adhesive may be placed in contact with a substrate or surfaceand the release liner may thereafter be stripped away from the adhesiveto expose another portion of the adhesive for bonding to anothersubstrate or surface. The adhesive article may be provided as a tape oran adhesive sheet which can be prepared by any of a variety of knownmethods such as by extruding, coating, or spraying the adhesivecomposition onto a backing layer. The pressure sensitive (meth)acrylicadhesive tape or sheet can be laminated onto a surface or substrate. Thetape or sheet can also be die-cut into any desired shape.

The present adhesive composition, derived from 2-octyl(meth)acrylate,provides comparable adhesive properties when compared with other isomersof octyl (meth)acrylate, such as n-octyl and isoctyl. Further, thepresent adhesive compositions have lower viscosities than adhesivesderived form other octyl isomers, such as isooctyl acrylate. The lowerviscosity compositions advantageously are easier to coat.

DETAILED DESCRIPTION

The adhesive composition comprises

a) a copolymer comprising:

-   -   1) 90 to 99.5 wt. % of 2-octyl(meth)acrylate, preferably 93 to        97 wt. %;    -   2) 0.5 to 10 wt. % of a carboxylic acid functional comonomer,        preferably (meth)acrylic acid;    -   3) less than 10 wt. % of other monomers, preferably less than 5        wt. %, relative to the amounts of 1) and 2); and

b) a crosslinking agent.

In certain preferred embodiments, the copolymer of the adhesivecomposition consists essentially of:

-   -   1) 90 to 99.5 wt. % of 2-octyl(meth)acrylate, preferably 93 to        97 wt. %;    -   2) 0.5 to 10 wt. % of a carboxylic acid functional comonomer,        preferably 1 to 7 wt. %.

The 2-octyl(meth)acrylate may be prepared by conventional techniquesfrom 2-octanol and (meth)acryloyl derivatives such as esters, acids andacyl halides. The 2-octanol may be prepared by treatment of ricinoleicacid, derived from castor oil, (or ester or acyl halide thereof) withsodium hydroxide, followed by distillation from the co-product sebacicacid.

Up to 10% by weight based on the total weight of monomers of othermonomers, such as monomers used to raise the T_(g) of the copolymer, maybe used in addition to monomers (1) and (2) above in the adhesivecopolymer. For example, ethylenically unsaturated monomers whosehomopolymers have a T_(g) of at least about 0° C., preferably greaterthan 20° C., may be used.

Examples of other monomers that may be co-polymerized with the(meth)acrylate ester and carboxylic acid-functional monomers include(meth)acrylamides, alpha-olefins, vinyl ethers, allyl ethers, styreneand other aromatic vinyl compounds, maleic acid esters,2-hydroxyethyl(meth)acrylate, cyclohexyl (meth)acrylate, t-butyl(meth)acrylate, phenyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate,N-vinyl pyrrolidone, N-vinyl caprolactam, and substituted(meth)acrylamides such as N-ethyl (meth)acrylamide, N-hydroxyethyl(meth)acrylamide, N-octyl(meth)acrylamide, N-t-butyl (meth)acrylamide,N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, andN-ethyl-N-dihydroxyethyl (meth)acrylamide.

The copolymerizable mixture may optionally further comprise chaintransfer agents to control the molecular weight of the resultantpolymer. Examples of useful chain transfer agents include but are notlimited to those selected from the group consisting of carbontetrabromide, alcohols, mercaptans, and mixtures thereof. When present,the preferred chain transfer agents are isooctylthioglycolate and carbontetrabromide. The polymerization mixture may further comprise up toabout 0.5 parts by weight of a chain transfer agent, typically about0.01 to about 0.5 parts by weight, if used, preferably about 0.05 partsby weight to about 0.2 parts by weight, based upon 100 parts by weightof the total monomer mixture.

However, the use of a chain transfer agent is generally not necessary.Applicants have discovered that the instant 2-octyl(meth)acrylateadhesives have generally lower inherent and solution viscosities whencompared to isomeric octyl(meth)acrylates, at the same concentrations,and under the same polymerization conditions. While not wishing to bebound by theory, it is believed that the instant octyl(meth)acrylates,having a tertiary hydrogen atom alpha to the ester hydroxyloxygen atom,serve as “internal” chain transfer agents to control the molecularweight.

In the practice of the invention, the copolymers can be polymerized bytechniques including, but not limited to, the conventional techniques ofsolvent polymerization, dispersion polymerization, and solventless bulkpolymerization, and radiation polymerization, including processes usingultraviolet light, electron beam, and gamma radiation. The monomermixture may comprise a polymerization initiator, especially a thermalinitiator or a photoinitiator of a type and in an amount effective topolymerize the comonomers.

Initiators useful in preparing the (meth)acrylate adhesive polymers usedin the present invention are initiators that, on exposure to heat orlight, generate free-radicals which initiate (co)polymerization of themonomer mixture. These initiators can be employed in concentrationsranging from about 0.0001 to about 3.0 pbw, preferably from about 0.001to about 1.0 pbw, and more preferably from about 0.005 to about 0.5 pbw,per 100 pbw of the monomer composition.

A typical solution polymerization method is carried out by adding themonomers, a suitable solvent, and an optional chain transfer agent to areaction vessel, adding a free radical initiator, purging with nitrogen,and maintaining the reaction vessel at an elevated temperature,typically in the range of about 40 to 100° C. until the reaction iscompleted, typically in about 1 to 20 hours, depending upon the batchsize and temperature. Examples of the solvent are methanol,tetrahydrofuran, ethanol, isopropanol, acetone, methyl ethyl ketone,methyl acetate, ethyl acetate, toluene, xylene, and an ethylene glycolalkyl ether. Those solvents can be used alone or as mixtures thereof.

Suitable initiators include but are not limited to those selected fromthe group consisting of azo compounds such as VAZO 64(2,2′-azobis(isobutyronitrile)), VAZO 52(2,2′-azobis(2,4-dimethylpentanenitrile)), and VAZO 67(2,2′-azobis-(2-methylbutyronitrile)) available from E.I. du Pont deNemours Co., peroxides such as benzoyl peroxide and lauroyl peroxide,and mixtures thereof. The preferred oil-soluble thermal initiator is(2,2′-azobis-(2-methylbutyronitrile)). When used, initiators maycomprise from about 0.05 to about 1 part by weight, preferably about 0.1to about 0.5 part by weight based on 100 parts by weight of monomercomponents in the pressure sensitive adhesive.

In a typical photopolymerization method, a monomer mixture may beirradiated with ultraviolet (UV) rays in the presence of aphotopolymerization initiator (i.e., photoinitiators). Preferredphotoinitiators are those available under the trade designationsIRGACURE and DAROCUR from Ciba Speciality Chemical Corp., Tarrytown,N.Y. and include 1-hydroxy cyclohexyl phenyl ketone (IRGACURE 184),2,2-dimethoxy-1,2-diphenylethan-1-one (IRGACURE 651),bis(2,4,6-trimethylbenzoyl)phenylphosphineoxide (IRGACURE 819),1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one(IRGACURE 2959), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone(IRGACURE 369),2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (IRGACURE907), and 2-hydroxy-2-methyl-1-phenyl propan-1-one (DAROCUR 1173).Particularly preferred photoinitiators are IRGACURE 819, 184 and 2959.

Solventless polymerization methods, such as the continuous free radicalpolymerization method described in U.S. Pat. Nos. 4,619,979 and4,843,134; the essentially adiabatic polymerization methods using abatch reactor described in U.S. Pat. No. 5,637,646; and, the methodsdescribed for polymerizing packaged pre-adhesive compositions describedin U.S. Pat. No. 5,804,610 may also be utilized to prepare the polymers.

The packaging material is made of a material that when combined with thebase copolymer or plasticized pressure sensitive adhesive compositiondoes not substantially adversely affect the desired pressure sensitiveadhesive characteristics. A hot melt coated pressure sensitive adhesiveproduced from a mixture of the pressure sensitive adhesive and thepackaging material may have improved pressure sensitive adhesiveproperties compared to hot melt coated pressure sensitive adhesiveproduced from pressure sensitive adhesive alone.

The packaging material should be appropriate for the polymerizationmethod used. For example, with photopolymerization, it is necessary touse a film material that is sufficiently transparent to ultravioletradiation at the wavelengths necessary to effect polymerization.Polymerization can be effected by exposure to ultraviolet (UV) radiationas described in U.S. Pat. No. 4,181,752. In a preferred embodiment, thepolymerization is carried out with UV black lights having over 60percent, and preferably over 75 percent of their emission spectrabetween 280 to 400 nanometers (nm), with an intensity between about 0.1to about 25 mW/cm².

In another preferred solventless polymerization method, the pressuresensitive adhesives of the present invention are prepared byphotoinitiated polymerization methods according to the techniquedescribed in U.S. Pat. No. 4,181,752, hereby incorporated by reference.The comonomers, and a photoinitiator are mixed together in the absenceof solvent and partially polymerized to a viscosity in the range of fromabout 500 cps to about 50,000 cps to achieve a coatable syrup.Alternatively, the monomers and photoinitiator are mixed in the absenceof solvent and partially polymerized to make a syrup. The plasticizingagent is then added to the syrup to make a coatable mixture for furtherpolymerization. In yet another way, the monomers, and plasticizing agentmay be mixed with a thixotropic agent such as fumed hydrophilic silicato achieve a coatable thickness. The crosslinking agent and any otheringredients are then added to the prepolymerized syrup or thickenedplasticized monomer mixture. Alternatively, these ingredients (with theexception of the crosslinking agent) can be added directly to themonomer mixture prior to pre-polymerization.

The resulting composition is coated onto a substrate (which may betransparent to ultraviolet radiation) and polymerized in an inert (i.e.,oxygen free) atmosphere, e.g., a nitrogen atmosphere by exposure toultraviolet radiation. Examples of suitable substrates include releaseliners (e.g., silicone release liners) and tape backings (which may beprimed or unprimed paper or plastic). A sufficiently inert atmospherecan also be achieved by covering a layer of the polymerizable coatingwith a plastic film which is substantially transparent to ultravioletradiation, and irradiating through that film in air as described in theaforementioned patent using ultraviolet lamps. Alternatively, instead ofcovering the polymerizable coating, an oxidizable tin compound may beadded to the polymerizable syrup to increase the tolerance of the syrupto oxygen as described in U.S. Pat. No. 4,303,485. The ultraviolet lightsource preferably has 90% of the emissions between 280 and 400 nm (morepreferably between 300 and 400 nm), with a maximum at 351 nm.

The first component polymer may be prepared (e.g., by solutionpolymerization followed by isolation). Any residual monomer and/orsolvents used in the preparation may be removed by conventionaltechniques such as distillation, vacuum evaporation, etc., to reduce theresidual content to less than 2 wt. %, prior to crosslinking. Thepolymerizations may be conducted in the presence of suitable solventssuch as ethyl acetate, toluene and tetrahydrofuran that are unreactivewith the acid or ester functional groups of the monomers.

In order to increase cohesive strength of the poly(meth)acrylatepressure sensitive adhesives, a crosslinking agent may be incorporatedinto the adhesive composition. Two main types of chemical crosslinkingagents are exemplary. The first crosslinking additive is a thermalcrosslinking agent such as multifunctional aziridine, isocyanate,oxazole and epoxy compounds. One example of aziridine crosslinker is1,1′-(1,3-phenylene dicarbonyl)-bis-(2-methylaziridine) (CAS No.7652-64-4). Other bisamide crosslinking agents are described in U.S.Pat. No. 6,893,718 (Melancon et al.), incorporated herein by reference.Common polyfunctional isocyanate crosslinkers are trimethylolpropanetoluene diisocyanate, toluene diisocyanate, and others known in the art.Such chemical crosslinkers can be added into solvent-based PSAs afterpolymerization and activated by heat during oven drying of the coatedadhesive.

Bisamide crosslinking agents may be of the formula

R¹ and R³ are independently selected from the group consisting of H andC_(n)H_(2n+1), where n is an integer ranging from 1 to 5,

R² is a divalent radical selected from the group consisting of phenyl,substituted phenyl, triazine, and —C_(n)H_(2m)—, where m is an integerranging from 1 to 10, and combinations thereof.

Multifunctional oxazoline crosslinking agents useful in this inventionare those that contain two or more groups per molecule selected from thegroup consisting of 2-oxazolines, 2 oxazines and combinations thereof.Preferred 1,3-oxazyl heterocyclic compounds are 1,3-oxazolines, and aparticularly preferred 1,3-oxazoline is 2-phenyl-2-oxazoline.Bisoxazolines are typically derived from polycarboxylic acids and suchpolycarboxylic acids include, but are not limited to aromatic acids; forexample, isophthalic acid, terephthalic acid, 5-t-butylisophthalic acid,trimesic acid, 1,2,4,5-benezenetetracarboxylic acid and 2,6-naphthalenedicarboxylic acid. The preferred polycarboxylic acids includeisophthalic acid, terephthalic acid and trimesic acid.

Polyfunctional 1,3-oxazyl heterocyclic compounds useful in thisinvention can be conveniently prepared by the reaction of thecorresponding esters of a polycarboxylic acids and alkanolamines.Nonlimiting examples of poly(1,3-oxazyl heterocyclic) compoundsincluding bisoxazolines are those having a nucleus represented by thefollowing Formula I:

wherein A is selected from the group consisting of a cyclic or acyclicaliphatic or substituted cyclic or acyclic aliphatic moiety having from1 to 20 carbon atoms or an aromatic (aryl) mono- or multinuclear oraliphatic substituted aryl residue having from 6 to 20 carbon atoms anda polymeric or oligomeric residue comprising from about 2 to 200,000repeating units;

R⁷ independently represents H, CH₃, CH₂CH₃, or C₆H₅;

R⁸ and R⁹ independently represent H or CH₃, preferably R⁷ and R⁹ are notboth CH₃;

x represents an integer of 0 or 1;

n is an integer of 2 or more, preferably 2 or 3.

Useful multifunctional oxazoline crosslinking agents include but is notlimited to 4,4′-5,5′-tetrahydro-2,2′-bisoxazole, (that is,2,2′-bis(2-oxazoline)); 2,2′-(alkanediyl)bis[4,5-dihydrooxazole], forexample, 2,2′-(1,4-butanediyl)bis[4,5-dihydrooxazole] and2,2′-(1,2-ethanediyl)bis[4,5-dihydrooxazole];2,2′-(arylene)bis[4,5-dihydrooxazole], e.g.,2,2′-(1,4-phenylene)bis[4,5-dihydrooxazole];2,2′-(1,5-naphthalenyl)bis[4,5-dihydrooxazole] and2,2′-(1,8-anthracenyl)bis[4,5-dihydrooxazole]; sulfonyl, oxy, thio oralkylene bis 2-(arylene)[4,5-dihydrooxazole], for example, sulfonyl bis2-(1,4-phenylene)bis[4,5-dihydrooxazole], oxybis2-(1,4-phenylene)bis[4,5-dihydrooxazole], thiobis2-(1,4-phenylene)bis[4,5-dihydrooxazole] and methylene bis2-(1,4-phenylene)bis[4,5-dihydrooxazole]; 2,2′,2″-(arylenetris[4,5-dihydrooxazole], e.g., 2,2′,2″-(1,3,5-phenylenetris[4,5-dihydrooxazole]; 2,2′,2″,2′″-(arylenetetra[4,5-dihydrooxazole], for example, 2,2′,2″,2″-(1,2,4,5-phenylenetetra[4,5-dihydrooxazole] and oligomeric and polymeric materials havingterminal oxazoline groups.

Typically, the relative amounts of (meth)acrylic acid co-monomer andcrosslinking agent is selected so that the ratio of the number ofequivalents of crosslinker functional groups (such as amide, oxazole,isocyanate or epoxy functional groups) to the number of equivalents ofcarboxylic acid groups is less than or equal to about 0.1. Moretypically, the ratio of the number of equivalents of amide groups to thenumber of equivalents of carboxylic acid groups is less than about 0.05,and generally will be between 0.0001 and 0.05. Most typically, the ratioof the number of equivalents of crosslinker functional groups to thenumber of equivalents of carboxylic acid groups will be between 0.0001and 0.05.

In another embodiment, chemical crosslinkers, which rely upon freeradicals to carry out the crosslinking reaction, may be employed.Reagents such as, for example, peroxides serve as a source of freeradicals. When heated sufficiently, these precursors will generate freeradicals which bring about a crosslinking reaction of the polymer. Acommon free radical generating reagent is benzoyl peroxide. Free radicalgenerators are required only in small quantities, but generally requirehigher temperatures to complete a crosslinking reaction than thoserequired for the bisamide and isocyanate reagents. The second type ofcrosslinking additive is a photosensitive crosslinker, which isactivated by high intensity ultraviolet (UV) light. Two commonphotosensitive crosslinkers used for (meth)acrylic PSAs are benzophenoneand copolymerizable aromatic ketone monomers as described in U.S. Pat.No. 4,737,559 (Kellen et al.). Another photocrosslinker, which can bepost-added to the solution polymer and activated by UV light is atriazine, for example,2,4-bis(trichloromethyl)-6-(4-methoxy-phenyl)-s-triazine. Thesecrosslinkers are activated by UV light generated from sources such asmedium pressure mercury lamps or a UV blacklight.

Useful polyisocyanates include aliphatic, alicyclic, and aromaticdiisocyanates, and mixtures thereof. A number of such diisocyanates arecommercially available. Representative examples of suitablediisocyanates include hexamethylene diisocyanate (HDT), trimethylhexamethylene diisocyanate (TMHDI), m- and p-tetramethylxylenediisocyanate (TMXDI), diphenylmethane diisocyanate (MDT), napthalenediisocyanate (NDI), phenylene diisocyanate, isophorone diisocyanate(IPDI), toluene diisocyanate (TDI), bis(4-isocyanatocyclohexyl) methane(H₁₂MDI), and the like, and mixtures thereof. Useful polyisocyanatesalso include derivatives of the above-listed monomeric polyisocyanates.These derivatives include, but are not limited to, polyisocyanatescontaining biuret groups, such as the biuret adduct of hexamethylenediisocyanate (HDI) available from Bayer Corp., Pittsburgh, Pa. under thetrade designation DESMODUR N-100, polyisocyanates containingisocyanurate groups, such as that available from Bayer Corp.,Pittsburgh, Pa. under the trade designation DESMODUR N-3300, as well aspolyisocyanates containing urethane groups, uretdione groups,carbodiimide groups, allophonate groups, and the like. If desired, smallamounts of one or more polyisocyanates having three or more isocyanategroups can be added to effect a degree of crosslinking. Preferredpolyisocyanates include aliphatic diisocyanates and derivatives thereof,with IPDI being most preferred.

Hydrolyzable, free-radically copolymerizable crosslinkers, such asmonoethylenically unsaturated mono-, di-, and trialkoxysilane compoundsincluding, but not limited to, methacryloxypropyltrimethoxysilane(available from Gelest, Inc., Tullytown, Pa.), vinyldimethylethoxysilane, vinyl methyl diethoxysilane, vinyltriethoxysilane,vinyltrimethoxysilane, vinyltriphenoxysilane, and the like, are alsouseful crosslinking agents. Crosslinking may also be achieved using highenergy electromagnetic radiation such as gamma or e-beam radiation. Inthis case, no crosslinker may be required.

Other additives can be included in the polymerizable mixture or added atthe time of compounding or coating to change the properties of thepressure sensitive adhesive. Such additives, include pigments,tackifiers, fillers such as glass or polymeric bubbles or beads (whichmay be expanded or unexpanded), hydrophobic or hydrophilic silica,calcium carbonate, glass or synthetic fibers, blowing agents, tougheningagents, reinforcing agents, fire retardants, antioxidants, andstabilizers. The additives are added in amounts sufficient to obtain thedesired end properties.

If other additives are used, then up to about 40% by weight, preferablyless than 30% by weight, and more preferably less than 5% by weightbased on the dry weight of the total adhesive polymer, would besuitable.

A wide variety of resinous (or synthetic) materials commonly used in theart to impart or enhance tack of pressure sensitive adhesivecompositions may be used as a tackifier (i.e., tackifying resin).Examples include rosin, rosin esters of glycerol or pentaerythritol,hydrogenated rosins, polyterpene resins such as polymerized beta-pinene,coumaroneindene resins, “C5” and “C9” polymerized petroleum fractions,and the like. The use of such tack modifiers is common in the art, as isdescribed in the Handbook of Pressure Sensitive Adhesive Technology,Second Edition, D. Satas, ed., Van Nostrand Reinhold, New York, N.Y.,1989. A tackifying resin is added in amounts required to achieve thedesired tack level. Examples of suitable commercially availabletackifiers include synthetic ester resins, such as that available underthe trade designation FORAL 85 from Hercules Inc., Wilmington, Del., andaliphatic/aromatic hydrocarbon resins, such as those available under thetrade designation ESCOREZ 2000 from Exxon Chemical Co., Houston, Tex.This is typically achieved by adding from 1 part to about 300 parts byweight of tackifying resin per 100 parts by weight of an acrylatecopolymer. The tackifying resin is selected to provide the acrylatecopolymers with an adequate degree of tack to maintain the resultantcomposition balanced pressure sensitive adhesive properties includingshear and peel adhesion. As is known in the art, not all tackifierresins interact with the acrylate copolymer in the same manner;therefore, some minor amount of experimentation may be required toselect the appropriate tackifier resin and to achieve optimum adhesiveperformance. Such minor experimentation is well within the capability ofone skilled in the adhesive art.

Plasticizing agents selected for use in the polymerizable compositionsof the present invention possess a range of properties. Generally, theplasticizing agents can be liquid or solid, have a range of molecularweights and architectures, are compatible with the base copolymers,monomeric or polymeric, non-volatile and non-reactive. Additionally,mixtures of solid and liquid, monomeric and polymeric and othercombinations of plasticizing agents can be used in the presentinvention.

Generally, liquid plasticizing agents are readily compoundable with thebase copolymers and/or can be chosen to be miscible with comonomers forplasticized pressure sensitive adhesive compositions prepared using bulkpolymerization methods. In addition, liquid plasticizing agents may bedelivered directly to non-tacky base copolymers or onto already coatedbase copolymer films and are typically absorbed quickly to activate thepressure sensitive adhesive properties.

Although somewhat more challenging to use, solid plasticizing agents canadvantageously be used in applications, processes or articles where thecontrolled plasticization of the base copolymer is desired. For example,hot melt processible pressure sensitive adhesive compositions can beeasily transported and handled prior to melt compounding if both thebase copolymer and plasticizing agent components are solid andnon-tacky. Once heated to the melting or glass transition temperature ofthe solid plasticizing agent, the base copolymer is plasticized and themixture exhibits pressure sensitive adhesive properties.

Additionally, the plasticizing agents can have a range of molecularweights and architectures. That is, the plasticizing agents can beeither polymeric or monomeric in nature. Typically, monomericplasticizing agents are derived from low molecular weight acids oralcohols, which are then esterified with respectively a monofunctionalalcohol or monofunctional acid. Examples of these are esters of mono-and multibasic acids, such as isopropyl myristate, dibutyl phthalate,diisoctyl phthalate, dibutyl adipate, dibutylsebacate and the like.Useful polymeric plasticizing agents are non-acrylic and are typicallyderived from cationically or free-radically polymerizable, condensationpolymerizable or ring-opening polymerizable monomers to make lowmolecular weight polymers. Examples of these polymeric plasticizingagents include materials such as polyurethanes, polyureas,polyvinylethers, polyethers, polyesters and the like. As used in thisapplication “non-acrylic” means the polymeric plasticizing agentcontains less than about 20% by weight of any (meth)acrylic monomers.

Additionally, useful plasticizing agents are non-reactive, thuspreventing copolymerization with the comonomers of the base copolymer.Thus, plasticizing agents having acrylate functionality, methacrylatefunctionality, styrene functionality, or other ethylenicallyunsaturated, free radically reactive functional groups are generally notused.

Particularly useful plasticizing agents include polyalkylene oxideshaving weight average molecular weights of about 150 to about 5,000,preferably of about 150 to about 1,500, such as polyethylene oxides,polypropylene oxides, polyethylene glycols; alkyl or aryl functionalizedpolyalkylene oxides, such as PYCAL 94 (a phenyl ether of polyethyleneoxide, commercially available from ICI Chemicals); benzoylfunctionalized polyethers, such as BENZOFLEX 400 (polypropylene glycoldibenzoate, commercially available from Velsicol Chemicals) andmonomethyl ethers of polyethylene oxides; monomeric adipates such asdioctyl adipate, dibutoxyethoxyethyl adipate and dibutoxypropoxypropyladipate; polymeric adipates such as polyester adipates; citrates, suchas acetyltri-n-butyl citrate, phthalates such as butyl benzylphthalates,trimellitates, sebacates, polyesters, such as those known under thetradename Paraplex (available from C.P. Hall Co); phosphate esters, suchas those known under the tradename of Santicizer (available from Ferro)such as 2-ethylhexyl diphenyl diphosphate and t-butylphenyl diphenylphosphate; glutarates such as Plasthall 7050 (a dialkyl dietherglutarate available from C.P. Hall Co.); and mixtures thereof.

The plasticizing agent may be used in amounts of from about 1 to 100parts by weight per 100 parts of the copolymer. In some embodiments, theplasticizing agent is present in amounts from about 3 to 50 pph. Mostpreferably, the plasticizing agent is present in amounts up to 10 wt. %plasticizer, relative to the weight of the copolymer.

The pressure sensitive adhesive composition can be applied to anysuitable substrate that can be a sheet, a fiber, or a shaped article.However, the preferred substrates are those used for pressure sensitiveadhesive products. The pressure sensitive adhesive composition can beapplied to at least one major surface of suitable flexible or inflexiblebacking materials before crosslinking is initiated.

The present invention further provides adhesive articles comprising thecured adhesive composition disposed on a backing or suitable substrate.In addition to a variety of traditional pressure sensitive adhesivearticles, such as tapes, labels, decals, transfer tapes and otherarticles the pressure sensitive adhesive article can be used indecorative, light management and optical articles.

Suitable materials useful as the flexible support or backing for theadhesive articles of the invention include, but are not limited to,polyolefins such as polyethylene, polypropylene (including isotacticpolypropylene), polystyrene, polyester, including poly(ethyleneterephthalate), polyvinyl chloride, poly(butylene terephthalate),poly(caprolactam), polyvinyl alcohol, polyurethane, poly(vinylidenefluoride), cellulose and cellulose derivates, such as cellulose acetateand cellophane, and the like. Commercially available backing materialsuseful in the invention include kraft paper (available from MonadnockPaper, Inc.); spun-bond poly(ethylene) and poly(propylene), such asTyvek™ and Typar™ (available from DuPont, Inc.); and porous filmsobtained from poly(ethylene) and poly(propylene), such as Teslin™(available from PPG Industries, Inc.), and Cellguard™ (available fromHoechst-Celanese).

Typical examples of flexible backing materials employed as conventionaltape backing that may be useful for the adhesive compositions includethose made of paper, plastic films such as polypropylene, polyethylene,polyester (e.g., polyethylene terephthalate), cellulose acetate, andethyl cellulose. Backings may also be prepared of fabric such as wovenfabric formed of threads of synthetic or natural materials such ascotton, nylon, rayon, glass, ceramic materials, and the like or nonwovenfabric such as air laid webs of natural or synthetic fibers or blends ofthese. The backing may also be formed of metal, metallized polymerfilms, or ceramic sheet materials may take the form of any articleconventionally known to be utilized with pressure sensitive adhesivecompositions such as labels, tapes, signs, covers, marking indicia, andthe like.

Preferably, the adhesive article comprises a backing of aliphaticpolyester. Aliphatic polyesters useful in the present invention includehomo- and copolymers of poly(hydroxyalkanoates) and homo- and copolymersof those aliphatic polyesters derived from the reaction product of oneor more alkanediols with one or more alkanedicarboxylic acids (or acylderivatives). Miscible and immiscible blends of aliphatic polyesterswith one or more additional semicrystalline or amorphous polymers mayalso be used.

One useful class of aliphatic polyesters are poly(hydroxyalkanoates),derived by condensation or ring-opening polymerization of hydroxy acids,or derivatives thereof. Suitable poly(hydroxyalkanoates) may berepresented by the formula H(O—R⁴—C(O)—)_(x)OH, where R⁴ is an alkylenemoiety having 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms,that may be linear or branched. “x” is a number such that the ester ispolymeric, and is preferably a number such that the molecular weight ofthe aliphatic polyester is 10,000 to 300,000 and is preferably fromabout 30,000 to 200,000. R⁴ may further comprise one or more catenary(i.e. in chain) ether oxygen atoms. Generally the R⁴ group of thehydroxyl acid is such that the pendant hydroxyl group is a primary orsecondary hydroxyl group.

Useful poly(hydroxyalkanoates) include, for example, homo- andcopolymers of poly(3-hydroxybutyrate), poly(4-hydroxybutyrate),poly(3-hydroxyvalerate), poly(lactic acid) (as known as polylactide),poly(3-hydroxypropanoate), poly(4-hydropentanoate),poly(3-hydroxypentanoate), poly(3-hydroxyhexanoate),poly(3-hydroxyheptanoate), poly(3-hydroxyoctanoate), polydioxanone, andpolycaprolactone, polyglycolic acid (also known as polyglycolide).Copolymers of two or more of the above hydroxy acids may also be used,for example, poly(3-hydroxybutyrate-co-3-hydroxyvalerate),poly(lactate-co-3-hydroxypropanoate) and poly(glycolide-co-p-dioxanone).Blends of two or more of the poly(hydroxyalkanoates) may also be used,as well as blends with one or more semicrystalline or amorphous polymer.

Another useful class of aliphatic polyesters includes those aliphaticpolyesters derived from the reaction product of one or more alkanediolswith one or more alkanedicarboxylic acids (or acyl derivatives). Suchpolyesters have the general formula

where R⁵ and R⁶ each represent an alkylene moiety that may be linear orbranched having from 1 to 20, preferably 1 to 12 carbon atoms, and z isa number such that the ester is polymeric, and is preferably a numbersuch that the molecular weight of the aliphatic polyester is 10,000 to300,000 and is preferably from about 30,000 to 200,000. Each y isindependently 0 or 1. R⁵ and R⁶ may further comprise one or morecatenary (i.e. in chain) ether oxygen atoms.

Examples of aliphatic polyesters include those homo- and copolymersderived from (a) one or more of the following diacids (or derivativethereof): succinic acid, adipic acid, 1,12 dicarboxydodecane, fumaricacid, and maleic acid and (b) one of more of the following diols:ethylene glycol, polyethylene glycol, 1,2-propane diol, 1,3-propanediol,1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol,1,6-hexanediol, diethylene glycol, and polypropylene glycol, and (c)optionally a small amount, i.e. 0.5-7.0 mole % of a polyol with afunctionality greater than two such as glycerol, neopentyl glycol, andpentaerythritol.

Such polymers may include polybutylenesuccinate homopolymer,polybutylene adipate homopolmer, polybutyleneadipate-succinatecopolymer, polyethylenesuccinate-adipate copolymer, polyethylene adipatehomopolymer.

Commercially available aliphatic polyesters include polylactide,polyglycolide, polylactide-co-glycolide, poly(L-lactide-co-trimethylenecarbonate), poly(dioxanone), poly(butylene succinate), and poly(butyleneadipate).

Especially useful aliphatic polyesters include those derived fromsemicrystalline polylactic acid. Polylactic acid (or polylactides) haslactic acid as its principle degradation product, which is commonlyfound in nature, is non-toxic and is widely used in the food,pharmaceutical and medical industries. The polymer may be prepared byring-opening polymerization of the lactic acid dimer, lactide. Lacticacid is optically active and the dimer appears in four different forms:L,L-lactide, D,D-lactide, D,L-lactide (meso lactide) and a racemicmixture of L,L- and D,D-. By polymerizing these lactides as purecompounds or as blends, polylactide polymers may be obtained havingdifferent stereochemistries and different physical properties, includingcrystallinity. The L,L- or D,D-lactide yields semicrystallinepolylactide and are preferred, while the polylactide derived from theD,L-lactide is amorphous.

Copolymers, including block and random copolymers, of poly(lactic acid)with other aliphatic polyesters may also be used. Useful co-monomersinclude glycolide, beta-propiolactone, tetramethyglycolide,beta-butyrolactone, gamma-butyrolactone, pivalolactone, 2-hydroxybutyricacid, alpha-hydroxyisobutyric acid, alpha-hydroxyvaleric acid,alpha-hydroxyisovaleric acid, alpha-hydroxycaproic acid,alpha-hydroxyethylbutyric acid, alpha-hydroxyisocaproic acid,alpha-hydroxy-beta-methylvaleric acid, alpha-hydroxyoctanoic acid,alpha-hydroxydecanoic acid, alpha-hydroxymyristic acid, andalpha-hydroxystearic acid.

Blends of poly(lactic acid) and one or more other aliphatic polyesters,or one or more other polymers may also be used in the present invention.Examples of useful blends include poly(lactic acid) and poly(vinylalcohol), polyethylene glycol/polysuccinate, polyethylene oxide,polycaprolactone and polyglycolide.

Useful polylactides may be prepared as described in U.S. Pat. No.6,111,060 (Gruber, et al.), U.S. Pat. No. 5,997,568 (Liu), U.S. Pat. No.4,744,365 (Kaplan et al.), U.S. Pat. No. 5,475,063 (Kaplan et al.), WO98/24951 (Tsai et al.), WO 00/12606 (Tsai et al.), WO 84/04311 (Lin),U.S. Pat. No. 6,117,928 (Hiltunen et al.), U.S. Pat. No. 5,883,199(McCarthy et al.), WO 99/50345 (Kolstad et al.), WO 99/06456 (Wang etal.), WO 94/07949 (Gruber et al.), WO 96/22330 (Randall et al.), WO98/50611 (Ryan et al.), U.S. Pat. No. 6,143,863 (Gruber et al.), U.S.Pat. No. 6,093,792 (Gross et al.), U.S. Pat. No. 6,075,118 (Wang etal.), and U.S. Pat. No. 5,952,433 (Wang et al.), the disclosure of eachU.S. patent incorporated herein by reference. Reference may also be madeto J. W. Leenslag, et al., J. Appl. Polymer Science, vol. 29 (1984), pp2829-2842, and H. R. Kricheldorf, Chemosphere, vol. 43, (2001) 49-54.

The above-described adhesive compositions are coated on a substrateusing conventional coating techniques modified as appropriate to theparticular substrate. For example, these compositions can be applied toa variety of solid substrates by methods such as roll, brush coating,flow, dip, spin, spray, knife, spread, wire, gravure, doctor blade anddie coating. These various methods of coating allow the compositions tobe placed on the substrate at variable thicknesses thus allowing a widerrange of use of the compositions.

The coating thickness will vary depending upon various factors such as,for example, the particular application, the coating formulation, andthe nature of the substrate (e.g., its absorbency, porosity, surfaceroughness, crepe, chemical composition, etc.). Coating thicknesses of2-250 micrometers (dry thickness), preferably about 25 to 200micrometers, are contemplated. The coatable adhesive composition may beof any desirable concentration for subsequent coating, but is typicallybetween 30 to 70 wt. % solids, and more typically between 50 and 35 wt.% solids, with the remainder solvent. The desired concentration may beachieved by further dilution of the adhesive composition, or by partialdrying. Generally, the adhesive composition is coated on the backing andheated to effect the crosslinking.

The flexible support or backing may also comprise a release-coatedsubstrate. Such substrates are typically employed when an adhesivetransfer tape is provided. Examples of release-coated substrates arewell known in the art. They include, by way of example, silicone-coatedkraft paper and the like. Tapes of the invention may also incorporate alow adhesion backsize (LAB). Typically this LAB is applied to the tapebacking surface that is opposite that bearing the pressure sensitiveadhesive. LABs are known in the art.

EXAMPLES

-   -   These examples are merely for illustrative purposes only and are        not meant to be limiting on the scope of the appended claims.        All parts, percentages, ratios, etc. in the examples and the        rest of the specification are by weight, unless noted otherwise.        Solvents and other reagents used were obtained from        Sigma-Aldrich Chemical Company; Milwaukee, Wis. unless otherwise        noted.

Table of Abbreviations Test Methods Peel Adhesion Testing

The peel adhesion test method used was similar to test method ASTM D3330-78 except that a glass substrate was used in place of stainlesssteel. Two 1.3 centimeter (0.5 inch) strips of sample tapes were adheredto a glass plate by rolling a 2 kilogram (4.5 pounds) roller onto thetape. The bonded assembly dwelled at room temperature for about oneminute and was tested for 180° peel adhesion using an IMASS slip/peeltester (Model 3M90, commercially available from Instrumentors Inc.,Strongsville, Ohio) at a rate of 229 centimeters per minute (90 inchesper minute). Peel force was measured in ounces per 0.5 inch andconverted to Newtons per decimeter (N/dm). The tests were run at 23° C.and 50% relative humidity unless otherwise specified.

Shear Strength Testing

The shear strength test method used was similar to test method ASTMD-3654-78, PSTC-7. Strips of sample tapes 1.3 centimeter (0.5 inch) widewere adhered to stainless steel plates and cut down to leave 1.3centimeter by 1.3 centimeter (0.5 inch by 0.5 inch) square on the steelplates. A weight of 2 kilograms (4.5 pounds) was rolled over the adheredportion. A weight of 1,000 grams was attached to each sample which wassuspended until the sample failed. The time of failure as well as themode of failure was noted (adhesive, cohesive, or mixed). Cohesivefailure means that adhesive is left both on the steel plate and thefilm, adhesive failure means that no adhesive is left on the steel plateand mixed means that some adhesive is left on the steel plate. Sampleswere run in triplicate and averaged. The tests were run at 23° C. and50% relative humidity unless otherwise specified. In some cases the sametest was run with fiberboard (FB) as the substrate.

Preparative Example 1 2-octyl acrylate

A mixture of 2-octanol (268.51 grams, 2.1 mol), AA (183.75 grams, 2.6mol), p-toluenesulfonic acid monohydrate (5.00 grams, 26 mmol), toluene(250 grams) and phenothiazine (1.0 grams) was heated to reflux. Waterwas separated from the toluene/water azeotrope using a Dean Starkdistillation trap. After six hours at reflux a total of 37 millilitersof water was collected in the trap. The reaction mixture was washed with1 Molar aqueous sodium hydroxide (200 milliliters), then concentratedunder reduced pressure. The remaining oil was distilled under reducedpressure (65-67° C. at 2 mmHg) to give the product as a colorless oil.(Yield: 248.6 grams)

Examples 1-2 and Comparative Examples C1-C2 Part 1: SolutionPolymerizations

For Examples 1 and 2 solution co-polymerizations of 2-OA with AA wereperformed by combining the materials shown in Table 1 in a glass jar,purging with nitrogen for 15 minutes, and sealing the jars. The jarswere placed in a 60° C. water bath oscillating at 110 rpm for 18-20hours. The same procedure was used for Comparative Examples C1 and C2except that IOA was used instead of 2-OA. The molecular weight (M_(w))and PDI of the resulting polymers were determined using GPC and theInherent viscosities (IV) were measured using a # 50 viscometer tube ata solution concentration of 0.5 grams/deciliter in THF. These data arepresented in Table 1 below.

TABLE 1 Ethyl 2-OA IOA AA VAZO 67 acetate M_(w) Example (grams) (grams)(grams) (grams) (grams) IV (grams/mole) PDI 1 23.75 — 1.25 0.025 37.50.9 3.7 × 10⁵ 3.8 2 23.25 — 1.75 0.025 37.5 1.0 3.9 × 10⁵ 4.1 C1 — 23.751.25 0.025 58.3 1.0 5.3 × 10⁵ 5.0 C2 — 23.25 1.75 0.025 37.5 1.7 7.7 ×10⁵ 6.2

Part 2: Preparation and Testing of Tape Samples

To prepare tape samples, 10.0 grams of the solutions prepared in Table 1above were placed into a vial along with the corresponding amount ofB-212 chemical crosslinker. The amount of B-212 in the formulations wasvaried from 0 to 0.3 weight % as shown in Table 2. The resultingsolutions were coated with a knife coater onto a primed PET film. Theknife height was set to 102-127 micrometers (4-5 mils) above thepolyester to get a coating that is about 25 micrometers (1 mil) whendried. The coated solution was allowed to air dry for 2 minutes toremove the solvent. The coated PET sheet was then taped onto a thinaluminum panel and placed into an oven at 70° C. for 5 minutes. Afterthe sample was removed from the oven, a release liner was placed on theadhesive to protect the coating. The coated films were allowed toequilibrate in a constant temperature/constant humidity (23° C./50%Relative Humidity) room for 24 hours prior to testing. The tape testingwas performed as described in the test methods above, the data arepresented in Table 2.

TABLE 2 B-212 Crosslinker Peel Level Adhesion Shear Strength Example (wt%) (N/dm) (minutes) 1-A 0 60 3 (cohesive) 1-B 0.1 56 463 (cohesive) 1-C0.3 47 238 (adhesive) 2-A 0 57 15 (cohesive) 2-B 0.1 58 5993 (cohesive)2-C 0.3 53 1015 (adhesive) C1-A 0 68 5 (cohesive) C1-B 0.1 57 72(cohesive) C1-C 0.3 43 136 (adhesive) C2-A 0 62 24 (cohesive) C2-B 0.162 5614 (cohesive) C2-C 0.3 50 4352 (mixed mode)

Examples 3-5 and Comparative Examples C3-C5 Part 1: SolutionPolymerizations

For Examples 3-5 solution co-polymerizations of 2-OA with AA wereperformed by combining the materials shown in Table 3 in a glass jar,purging with nitrogen for 15 minutes, and sealing the jars. The jarswere placed in a 60° C. water bath oscillating at 110 rpm for 24 hours.The same procedure was used for Comparative Examples C3-C5 except thatIOA was used instead of 2-OA. The Inherent viscosities (IV) weremeasured using a # 50 viscometer tube at a solution concentration of 0.5grams/deciliter in THF. Brookfield viscosity was measured at roomtemperature using a Brookfield viscometer (measured in centipoise andconverted to Pascal Seconds). These data are presented in Table 3 below.

TABLE 3 Ex- VAZO Ethyl Brookfield am- 2-OA IOA AA 67 acetate Viscosityple (grams) (grams) (grams) (grams) (grams) (Pa s) IV 3 17.10 — 0.900.018 42.0 0.46 0.87 4 19.95 — 1.05 0.021 39.0 1.60 1.08 5 22.8  — 1.200.024 36.0 12 1.29 C3 — 17.10 0.90 0.018 42.0 0.86 1.06 C4 — 19.95 1.050.021 39.0 5.2 1.34 C5 — 22.8  1.20 0.024 36.0 52 1.66

Examples 6-7 and Comparative Examples C6-C7 Part 1: SolutionPolymerizations

For Examples 6-7 solution co-polymerizations of 2-OA with AA wereperformed as described in Examples 1-2 with the weight ratios ofmonomers shown in Table 4. The same procedure was used for ComparativeExamples C6-C7 except that IOA was used instead of 2-OA.

Part 2: Preparation and Testing of Thermal Stability Samples

To prepare thermal stability testing samples, solution polymers withvarying compositions were prepared following the general proceduredescribed in Part 1 above. The polymer solutions were then placed into avial along with the corresponding amount of B-212 chemical crosslinker.The weight % of B-212 is shown in Table 4. This solution was coated witha knife coater onto a silicone release liner. The knife height was setto 254 micrometers (10 mils) above the liner. The coated solution wasallowed to air dry for 5 minutes to remove the solvent. The coated filmwas then taped onto a thin aluminum panel and placed into an oven at150° C. for 2 minutes. The coated adhesives were allowed to equilibratein constant temperature/constant humidity (CT/CH) room for 24 hoursprior to testing. To determine the degradation onset temperature, asample of the adhesive (approximately 20-30 milligrams) was analyzedusing a TA Instruments TGA 2950 Thermogravimetric Analyzer (TAInstruments Inc., New Castle, Del.). The sample was subjected to atemperature ramp from room temperature to 500° C. at a rate of 10°C./min. The onset point of degradation was then determined from thesample weight versus temperature plot (calculated using the TAInstruments Universal Analysis software). In addition, the thermalstability of the adhesives at 150° C. and 175° C. were determined. Usingthe TA Instruments TGA 2950 Thermogravimetric Analyzer, the sampletemperature was increased from room temperature to the desired set point(either 150° C. or 175° C.) at 200° C./min and kept at the set point for3.5 hrs. The sample weight was monitored and the % weight loss after 3.5hrs was determined based on the original weight of the sample. The dataare presented in Table 4.

TABLE 4 Weight Weight loss loss at at 175° C. Degradation 150° C. forfor 3.5 Onset 2-OA IOA AA B-212 3.5 hours hours Temperature Example (wt%) (wt %) (wt %) (wt %) (%) (%) (° C.) 6 95 — 5 0.1 1.0 9.1 313 C6 — 955 0.1 3.6 12.7 352 7 90 — 10 0.1 1.3 4.2 307 C7 — 90 10 0.1 2.3 4.0 339

Examples 8-11 Part 1: Solution Polymerizations

For Examples 8-11 solution co-polymerizations of 2-OA with AA wereperformed as described in Examples 1-2 above with the weight ratiosshown in Table 5.

Part 2: Preparation and Testing of Tape Samples

To prepare tape samples, portions of the solutions prepared in Part 1above were placed into a vial along with the corresponding amount ofB-212 chemical crosslinker and SANTICIZER 141 plasticizer as shown inTable 5. These mixtures were coated on PLA film with a knife coaterusing the method described in Examples 1-2. The coated solution wasallowed to air dry for 2 minutes to remove the solvent. The coated filmwas then taped onto a thin aluminum panel and placed into an oven at 70°C. for 5 minutes. A release liner was then placed over the coatedadhesives and they were allowed to equilibrate in constanttemperature/constant humidity (CT/CH) room for 24 hours prior totesting. Shear strength testing on both stainless steel (SS) and fiberboard (FB) substrates was performed as described in the test methodsabove and the results are shown in Table 5.

TABLE 5 Shear Shear 2-OA AA B-212 SANTICIZER Strength on Strength on FBExample (wt %) (wt %) (wt %) 141 (wt %) SS (minutes) (minutes) 8 95 50.1 0 6706 359 9 95 5 0.1 1.0 8478 167 10 95 5 0.1 1.5 6648 479 11 95 50.1 2.0 5266 440

1. An adhesive composition comprising a copolymer comprising thereaction product of: 1) 90 to 99.5 wt. % of 2-octyl(meth)acrylate; 2)0.5 to 10 wt. % of a (meth)acrylic acid comonomer; and 3) less than 10wt. % of other monomers, relative to the combined weight of 1) and 2).2. The adhesive of claim 1, wherein the other monomers are primary octylacrylates.
 3. The adhesive of claim 1, wherein the (meth)acrylic acidcomonomer is selected from the group consisting of acrylic acid,methacrylic acid, and combinations thereof.
 4. An adhesive articlecomprising the adhesive of claim 1 and a backing.
 5. The adhesivearticle of claim 4, wherein the backing is selected from polyolefins,polystyrene, polyester, polyvinyl chloride, polyvinyl alcohol,polyurethane, poly(vinylidene fluoride), cellulose and cellulosederivatives.